/**********************************************************************\
* To commemorate the 1996 RSA Data Security Conference, the following  *
* code is released into the public domain by its author.  Prost!       *
*                                                                      *
* This cipher uses 16-bit words and little-endian byte ordering.       *
* I wonder which processor it was optimized for?                       *
*                                                                      *
* Thanks to CodeView, SoftIce, and D86 for helping bring this code to  *
* the public.                                                          *
\**********************************************************************/

#include <string.h>
#include <assert.h>

/**********************************************************************\
* Expand a variable-length user key (between 1 and 128 bytes) to a     *
* 64-short working rc2 key, of at most "bits" effective key bits.      *
* The effective key bits parameter looks like an export control hack.  *
* For normal use, it should always be set to 1024.  For convenience,   *
* zero is accepted as an alias for 1024.                               *
\**********************************************************************/

void rc2_keyschedule( unsigned short xkey[64],
                     const unsigned char *key,
                     unsigned len,
                     unsigned bits )
{
    unsigned char x;
    unsigned i;
    /* 256-entry permutation table, probably derived somehow from pi */
    static const unsigned char permute[256] = {
        217,120,249,196, 25,221,181,237, 40,233,253,121, 74,160,216,157,
        198,126, 55,131, 43,118, 83,142, 98, 76,100,136, 68,139,251,162,
        23,154, 89,245,135,179, 79, 19, 97, 69,109,141,  9,129,125, 50,
        189,143, 64,235,134,183,123, 11,240,149, 33, 34, 92,107, 78,130,
        84,214,101,147,206, 96,178, 28,115, 86,192, 20,167,140,241,220,
        18,117,202, 31, 59,190,228,209, 66, 61,212, 48,163, 60,182, 38,
        111,191, 14,218, 70,105,  7, 87, 39,242, 29,155,188,148, 67,  3,
        248, 17,199,246,144,239, 62,231,  6,195,213, 47,200,102, 30,215,
        8,232,234,222,128, 82,238,247,132,170,114,172, 53, 77,106, 42,
        150, 26,210,113, 90, 21, 73,116, 75,159,208, 94,  4, 24,164,236,
        194,224, 65,110, 15, 81,203,204, 36,145,175, 80,161,244,112, 57,
        153,124, 58,133, 35,184,180,122,252,  2, 54, 91, 37, 85,151, 49,
        45, 93,250,152,227,138,146,174,  5,223, 41, 16,103,108,186,201,
        211,  0,230,207,225,158,168, 44, 99, 22,  1, 63, 88,226,137,169,
        13, 56, 52, 27,171, 51,255,176,187, 72, 12, 95,185,177,205, 46,
        197,243,219, 71,229,165,156,119, 10,166, 32,104,254,127,193,173
    };

    assert(len > 0 && len <= 128);
    assert(bits <= 1024);
    if (!bits)
        bits = 1024;

    memcpy(xkey, key, len);

    /* Phase 1: Expand input key to 128 bytes */
    if (len < 128) {
        i = 0;
        x = ((unsigned char *)xkey)[len-1];
        do {
            x = permute[(x + ((unsigned char *)xkey)[i++]) & 255];
            ((unsigned char *)xkey)[len++] = x;
        } while (len < 128);
    }

    /* Phase 2 - reduce effective key size to "bits" */
    len = (bits+7) >> 3;
    i = 128-len;
    x = permute[((unsigned char *)xkey)[i] & (255 >> (7 & -bits))];
    ((unsigned char *)xkey)[i] = x;

    while (i--) {
        x = permute[ x ^ ((unsigned char *)xkey)[i+len] ];
        ((unsigned char *)xkey)[i] = x;
    }

    /* Phase 3 - copy to xkey in little-endian order */
    i = 63;
    do {
        xkey[i] =  ((unsigned char *)xkey)[2*i] +
            (((unsigned char *)xkey)[2*i+1] << 8);
    } while (i--);
}

/**********************************************************************\
* Encrypt an 8-byte block of plaintext using the given key.            *
\**********************************************************************/

void rc2_encrypt( const unsigned short xkey[64],
                 const unsigned char *plain,
                 unsigned char *cipher )
{
    unsigned x76, x54, x32, x10, i;

    x76 = (plain[7] << 8) + plain[6];
    x54 = (plain[5] << 8) + plain[4];
    x32 = (plain[3] << 8) + plain[2];
    x10 = (plain[1] << 8) + plain[0];

    for (i = 0; i < 16; i++) {
        x10 += (x32 & ~x76) + (x54 & x76) + xkey[4*i+0];
        x10 = (x10 << 1) + (x10 >> 15 & 1);

        x32 += (x54 & ~x10) + (x76 & x10) + xkey[4*i+1];
        x32 = (x32 << 2) + (x32 >> 14 & 3);

        x54 += (x76 & ~x32) + (x10 & x32) + xkey[4*i+2];
        x54 = (x54 << 3) + (x54 >> 13 & 7);

        x76 += (x10 & ~x54) + (x32 & x54) + xkey[4*i+3];
        x76 = (x76 << 5) + (x76 >> 11 & 31);

        if (i == 4 || i == 10) {
            x10 += xkey[x76 & 63];
            x32 += xkey[x10 & 63];
            x54 += xkey[x32 & 63];
            x76 += xkey[x54 & 63];
        }
    }

    cipher[0] = (unsigned char)x10;
    cipher[1] = (unsigned char)(x10 >> 8);
    cipher[2] = (unsigned char)x32;
    cipher[3] = (unsigned char)(x32 >> 8);
    cipher[4] = (unsigned char)x54;
    cipher[5] = (unsigned char)(x54 >> 8);
    cipher[6] = (unsigned char)x76;
    cipher[7] = (unsigned char)(x76 >> 8);
}

/**********************************************************************\
* Decrypt an 8-byte block of ciphertext using the given key.           *
\**********************************************************************/

void rc2_decrypt( const unsigned short xkey[64],
                 unsigned char *plain,
                 const unsigned char *cipher )
{
    unsigned x76, x54, x32, x10, i;

    x76 = (cipher[7] << 8) + cipher[6];
    x54 = (cipher[5] << 8) + cipher[4];
    x32 = (cipher[3] << 8) + cipher[2];
    x10 = (cipher[1] << 8) + cipher[0];

    i = 15;
    do {
        x76 &= 65535;
        x76 = (x76 << 11) + (x76 >> 5);
        x76 -= (x10 & ~x54) + (x32 & x54) + xkey[4*i+3];

        x54 &= 65535;
        x54 = (x54 << 13) + (x54 >> 3);
        x54 -= (x76 & ~x32) + (x10 & x32) + xkey[4*i+2];

        x32 &= 65535;
        x32 = (x32 << 14) + (x32 >> 2);
        x32 -= (x54 & ~x10) + (x76 & x10) + xkey[4*i+1];

        x10 &= 65535;
        x10 = (x10 << 15) + (x10 >> 1);
        x10 -= (x32 & ~x76) + (x54 & x76) + xkey[4*i+0];

        if (i == 5 || i == 11) {
            x76 -= xkey[x54 & 63];
            x54 -= xkey[x32 & 63];
            x32 -= xkey[x10 & 63];
            x10 -= xkey[x76 & 63];
        }
    } while (i--);

    plain[0] = (unsigned char)x10;
    plain[1] = (unsigned char)(x10 >> 8);
    plain[2] = (unsigned char)x32;
    plain[3] = (unsigned char)(x32 >> 8);
    plain[4] = (unsigned char)x54;
    plain[5] = (unsigned char)(x54 >> 8);
    plain[6] = (unsigned char)x76;
    plain[7] = (unsigned char)(x76 >> 8);
}

